1. Field of the Invention
The present invention relates to a zone controlled conveyor system, and more specifically to a system for the purpose of enabling an accurate stop of an article at a target position. Further, the present invention relates to an improvement of a zone controller for use in the zone controlled conveyor system.
2. Description of the Related Art
Recently, a zone controlled conveyor system that has a conveying line consisting of a plurality of control zones (zones for control), each zone having a zone controller for controlling conveyance of articles has been developed.
A patent document 1 specified below discloses such a conveyor system.
The conventional conveyor system that is disclosed in the patent document 1 includes at least one driving roller and free rollers for conveyance connected by belts spanned over them in each unit. Each unit has a presence sensor for detecting the presence of an article and a zone controller for controlling operation of the driving roller.
The zone controllers of each unit, connected electrically to others, drives and halts operation of the driving roller depending on presence signals of an article of its home control zone (i.e., the zone corresponding to the zone controller) and taking into account signals such as the presence signal transmitted from upstream and downstream control zones. That is, according to the conventional system, such cooperative control by zone controllers achieves the “zero-pressure accumulating control” that enables articles avoiding collision therebetween.
Patent Document 1: Japanese Laid-Open Patent Application No. Hei. 11-199030.
However, the conventional system has caused problems in relation to a halt of articles.
As to the conventional system, in order to stop an article, when the sensor detects it, it makes an abrupt stop of the driving roller that is driven at a prescribed standard conveying speed at that time. An unexpected inertial force resulting from the abrupt stop of the driving roller acts on the article, so that the inertial force of the article turns the driving roller that has been stopped being driven, hindering a stable stop of the article at the target position.
Further, due to the inertia force acted on an article by the abrupt stop of the driving roller, the article slips on the conveyor, increasing instability of its stop position.
Still further, as to the conventional system, due to an ununiform friction between an article and the roller, the article irregularly slips on the conveyor, hindering uniform orientations of the stopped article.
The invention disclosed in the application is proposed in consideration of the above-mentioned situations, aiming to provide a zone controlled conveyor system that enables an accurate and stable stop of articles at a target position. Further, the present invention is proposed aiming to provide a zone controller for suitable use in the zone controlled conveyor system.